THE MUSCULAR SYSTEM 133
which lies between the acromion and the upper end of the humerus. Branches of the circumflex arteries and nerve enter the deep surface. It fuses to a greater or less extent with the braehialis anticus (Humphry 340; Macalister 350; Sonntag 399). The fibres converge to the common deltoid insertion into the upper part of the shaft of the humerus.
Scapular Muscles.—The infraspinatus is larger than the supraspinatus, The supraspinatus, infraspinatus and subscapularis arise from the whole of the fossse wherein they lie; and they are all inserted into the tuberosities of the humerus as in Man, The teres major springs from the inner half of the axillary border of the scapula, and it is inserted into the humerus at the root of the pectoral crest. The teres minor arises as follows:—
Gibbon: lower border of lip of glenoid cavity and outer inch of scapular border.
Chimpanzee: lower border of lip of glenoid cavity and outer two-thirds of scapular border.
Orang: lower border of lip of glenoid cavity and outer half of scapular border.
Gorilla: lower border of lip of glenoid cavity and outer third of scapular border.
Man: as in Chimpanzee.
The insertion is practically identical in the Apes and in Man.
All the muscles of the shoulder-girdle are innervated as in Man, but they can produce a wider range of movement in the Apes.
The serratus magnus arises by digitations, or by a continuous linear origin from the outer surfaces of a